The Adh gene in Drosophila and its ultimate product ADH, are being analyzed in an effort to clarify the mechanism of gene regulation in a higher organism. This particular system has several attributes that make it suitable for this kind of analysis. ADH is a relatively simple protein whose sequence will soon be published. It is easily purified and available in large quantities. It appears to be unessential for survival. In addition, chemical selection procedures have been developed that allow mutations, revertants, and recombinants to be detected with great sensitivity. Over 50 mutants affecting ADH activity are available for analysis. I propose five lines of attack. 1. A new selection procedure will be utilized to search for overproducer mutants 2. The synthesis and degradation of ADH will be probed. 3. ADH mRNA will be isolated and used to measure the number of Adh genes and the concentration of ADH mRNA. 4. The Adh-mutants will be surveyed for nonsense suppressible mutants by an in vitro test. 5. Intracistronic mapping of Adh-negatives will be continued.